1. Field of the Invention
The present invention relates to a compact dielectric resonator of a very high value of Q, to a dielectric filter making use of the resonator, to a dielectric duplexer and to a communications device.
2. Background Art
Recently, dielectric resonators utilizing a dielectric as a material for constructing the resonator have been widely used so as to miniaturize the resonant system of an electric circuit which handles high-frequency waves such as microwaves. Such dielectric resonators utilize the phenomenon that the wavelength of an electromagnetic wave in a dielectric is 1/(∈r)xc2xd(wherein ∈r represents relative dielectric constant) that measured in free space. Dielectric resonators are used in a variety of resonant modes, including the TE, TM and TEM modes. In order to prevent electromagnetic energy from being scattered and lost, dielectric resonators are usually housed in a metallic casing, or alternatively, metal electrodes are formed on the dielectric surface.
In resonant systems of the above-mentioned types, Qu (i.e., Q under no-load) varies not only depending on Qd (=1/tan xcex4, Q of the dielectric per se) but also on Qc (i.e., Q attributed to a conductor loss which is caused by the current that flows in the surface of metal). Qu is expressed by the following equation: 1/Qu=(1/Qd)+(1/Qc). Therefore, in order to realize a resonant system of a high Qu, it is essential that a dielectric material of high Qd be used, and in addition, it is essential that electrodes of high Qcxe2x80x94in other words, electrodes of small conductor lossxe2x80x94be used.
Japanese Patent Application Laid-Open (kokai) No. 1-154603 discloses a method for achieving a high Qu (Q under no-load) by forming RExe2x80x94Mxe2x80x94Cuxe2x80x94O-based superconducting electrodes on a dielectric ceramic of any of a variety of types, including MgTiO3xe2x80x94(Ca, Me)TiO3-based dielectric ceramic, Ba(Zr, Zn, Ta)O3-based dielectric ceramic, (Zr, Sn)TiO4 and BaOxe2x80x94PbOxe2x80x94Nd2O3xe2x80x94TiO2-based dielectric ceramic. Also, Japanese Patent Application Laid-Open (kokai) No. 9-298404 discloses a method which utilizes Ba(Mg, Ta)O3 as a dielectric material.
FIGS. 1 and 2 are graphs showing temperature-dependent characteristics of tan xcex4(=1/Qd) at 10 GHz for a variety of dielectric materials. As shown in FIGS. 1 and 2, MgTiO3xe2x80x94(Ca, Me)TiO3-based material, Ba(Zr, Zn, Ni, Ta)O3-based material, BaOxe2x80x94PbOxe2x80x94Nd2O3xe2x80x94TiO2-based material, and Ba(Mg, Ta)O3-based material exhibit disadvantageously poor low-temperature characteristics because in each case, tan xcex4 does not decrease at a constant rate across an entire range of low temperatures.
In a (Zr, Sn)TiO4-based dielectric material, tan xcex4 decreases at a constant rate throughout the low temperature range. However, this material has a disadvantage in that a violent interface reaction occurs between the resultant dielectric and superconducting electrodes. Particularly when a thick film is formed through screen printing, interfacial reaction between a dielectric and oxide superconducting material raises a critical issue; violent interfacial reaction degrades the superconducting material and therefore no superconducting characteristic can be obtained. Therefore, in order to pursue practical use of various products derived from superconducting materials, there exists a strong need for a new substrate material that does not cause interfacial reaction. MgO is a candidate dielectric material that does not cause interfacial reaction between the dielectric and oxide superconducting material, and thus is suitable for use with high-frequency waves. However, MgO has an ∈r (relative dielectric constant) of 9-10, which is low as compared to that of the above-mentioned dielectric (∈r=20-30), making MgO disadvantageous in terms of miniaturizing the resonant system.
Accordingly, a primary object of the present invention is to provide a compact dielectric resonator of high Qu, in which an electrode formed of oxide superconducting material is provided on a surface of the dielectric.
Another object of the present invention is to provide a dielectric filter making use of such a compact resonator.
A further object of the present invention is to provide a dielectric duplexer making use of the compact resonator.
A still further object of the present invention is to provide a communications device making use of the compact resonator.
In a first aspect of the present invention, there is provided a dielectric resonator comprising a dielectric and an oxide superconducting electrode provided on a surface of the dielectric, wherein the dielectric is a Ba(Mg, Ma)O3-based dielectric (wherein Ma is at least one pentavalent elemental metal but cannot be Ta alone), and the oxide superconducting electrode is formed of an oxide superconducting material selected from among a RExe2x80x94Mxe2x80x94Cuxe2x80x94O-based oxide superconducting material (wherein RE is a rare earth element and M is an alkaline earth metal element), a Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material (which encompasses those in which Bi is partially substituted by Pb), and a Tlxe2x80x94Baxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material.
Preferably, Ma is at least one element selected from among Ta, Sb and Nb (except the case where Ta is used alone).
In a second aspect of the present invention, there is provided a dielectric resonator comprising a dielectric and an oxide superconducting electrode provided on a surface of the dielectric, wherein the dielectric is a Ba(Mb, Mg, Ta)O3-based dielectric (wherein Mb is a tetravalent or pentavalent elemental metal), and the oxide superconducting electrode is formed of an oxide superconducting material selected from among a RExe2x80x94Mxe2x80x94Cuxe2x80x94O-based oxide superconducting material (wherein RE is a rare earth element and M is an alkaline earth metal element), a Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material (which encompasses those in which Bi is partially substituted by Pb), and a Tlxe2x80x94Baxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material.
Preferably, Mb is at least one element selected from among Sn, Zr, Sb and Nb.
Preferably, the Ba(Mb, Mg, Ta)O3-based dielectric is a Ba(Sn, Mg, Ta)O3-based dielectric. Preferably, the composition of the Ba (Sn, Mg, Ta)O3-based dielectric is Ba(Snx, Mgy, Taz)O7/2xe2x88x92x/2xe2x88x923y/2 (wherein x+y+z=1, 0.04xe2x89xa6xxe2x89xa60.26, 0.23xe2x89xa6yxe2x89xa60.31, and 0.51xe2x89xa6zxe2x89xa60.65).
In a dielectric resonator according to the second aspect of the present invention, the Ba(Mb, Mg, Ta)O3-based dielectric may be a Ba(Mg, Sb, Ta)O3-based dielectric. In this case, the composition of the Ba(Mg, Sb, Ta)O3-based dielectric is BaxMgy(Sbv, Talxe2x88x92v)zOw (wherein x+y+z=1, w is an arbitrary number, x, y, and z fall within the tetrahedron defined by connecting points A, B, C, and D shown in Table 1, and 0.00xe2x89xa6vxe2x89xa60.300).
In the first and second aspects of the present invention, the RExe2x80x94Mxe2x80x94Cuxe2x80x94O-based oxide superconducting material may be YBa2Cu3O7-x, the Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material may be (Bi,Pb)2Sr2Ca2CU3Ox or Bi2, Sr2CaCu2Ox, and the Tlxe2x80x94Baxe2x80x94Caxe2x80x94Cuxe2x80x94O-based oxide superconducting material may be Tl2Ba2Ca2Cu3Ox.
In a third aspect of the present invention, there is provided a dielectric filter comprising a dielectric resonator according to any of the above aspects of the present invention, and an external connecting means.
In a fourth aspect of the present invention, there is provided a dielectric duplexer comprising at least two dielectric filters, input-output connection means for each of the dielectric filters, and antenna connecting means which is connected to the dielectric filter, wherein at least one of the dielectric filters is a dielectric filter of the present invention.
In a fifth aspect of the present invention, there is provided a communications device comprising a dielectric duplexer as described above, a transmitting circuit which is connected to at least one input-output connection means of the dielectric duplexer, a receiving circuit which is connected to at least one input-output connection means other than that to be connected to the transmitting circuit, and an antenna which is connected to the antenna connecting means of the dielectric duplexer.
Examples of the RE element that serves as a constituent of the RExe2x80x94Mxe2x80x94Cuxe2x80x94O-based oxide superconducting material include Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. M (i.e., an alkaline earth metal element) is preferably Ba or Sr among others.
Since the surface resistance (Rs) of an oxide superconducting material is lower than that of metal at a temperature lower than a critical temperature (Tc), smaller conductor loss occurs in electrodes, to thereby greatly improve Qc. Also, the dielectric used in the present invention exhibits an excellent tan xcex4 characteristic at a low temperature, and does not cause interfacial reaction with an oxide superconducting material. Therefore, the dielectric of the present invention is suitable for forming an oxide superconducting electrode on the surface thereof.